All posts by Steve Donaldson
Below are all of Steve Donaldson's postings, with the most recent are at the bottom of the page.
Alan : This has to be something in your local area, some electrical appliance or device, emitting interference. It must also be one which is timed, hence it always occurs at the same time.
Use a battery-powered AM radio to track down the source. Tune away from a station. Have the radio turned on before the interference occurs and the TV on, tuned to a channel on the C27 mux. You might hear the noise begin on the radio at the same time the quality of the TV signal goes to zero. You then know you are hearing the source that is knocking out the TV. Move around with the radio in effort to locate the source. Be aware that an AM radio doesn't use a pull-up whip antenna, as with FM. Instead, it uses a ferrite rod inside the set. This is directional and you can use this to your advantage when locating the source, but understand how it works first:
The aerial is most sensitive perpendicular to the set. It is least sensitive at each end. What this means is if you tune in to a station (on AM) then spin the radio round, keeping it horizontal, you will find that the audio goes fainter/weaker and stronger as you rotate. When it is at its strongest you have the radio facing or with its back to the source (the transmitter). When you rotate it 90 (keeping it horizontal), the sound will go to its lowest/weakest. The signal is therefore coming from the direction at one ends of the set. Come to understand this and use the same technique to locate the source. Bear in mind that it could be above you, either directly above or diagonally above.
How long does the break in reception go on for? The longer, the better because it gives longer to find the source.
I am reminded of a three-way port valve that switched the water flow between hot water and central heating, or both. When it was activated it would obliterate reception of an FM station for 20 seconds or so.
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Steve Donaldson: See this video of a radio ham tracking a source of interference in his house. Early on he shows how rotating the radio to where the sound is at is lowest/least means that the source is in a direction that one or other end of the set is pointing:
Tracking Interference Using A Portable AM Radio With Ferrite Antenna - YouTube
Having surveyed a number of locations, he triangulated the location of the source.
Bear in mind that the noise could be emanating from something at a neighbour's.
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Roger F C Alban: The first thing to do is confirm that you are in fact tuned to Mendip, and not Wenvoe, which is in the exact opposite direction and could be being picked up off the back of your aerial.
The signal strength screen usually gives the tuning information. It should be tuned to UHF channel 33 (570MHz). If it is tuned to UHF channel 45 (666MHz) then it is tuned to Wenvoe.
The only other possibility as to wrong tuning is that the signal is coming from Stockland Hill. This isn't to say it is in any way likely, but if you find it tuned to UHF channel 22 (482MHz) then it's Stockland Hill you've got.
If it's tuned to the wrong transmitter then the next step is to correct this. It's always possible that it could be tuned wrong for other channels but they give good reception. You can check the full six multiplexes if you like, the list for Mendip is:
PSB1 [BBC One] = C32
PSB2 [ITV1] = C34
PSB3 [BBC One HD] = C35
COM4 [16 QVC] = C48
COM5 [Sky News] = C33
COM6 [12 Quest] = C36
There are six multiplexes, which are a single signal carrying multiple programme channels, e.g. all BBC standard definition are on PSB1. The above gives one such programme channel on the respective multiplex, written in square brackets, and this can be used to see what UHF channel is tuned. The UHF channel numbers are prefixed "C".
The six Wenvoe UHF channels, in respective order, are 41, 44, 47, 42, 45 and 39. Stockland Hill's are 26, 23, 29, 25, 22 and 28.
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Sharon Simms: This really sounds like a transmitter fault. The multiplex which carries these services is operated by Digital 3&4 Limited, which is a consortium of ITV and Channel 4.
You can find contact details on the Ofcom website under multiplex licensees:
Multiplex licensees - Ofcom
It gives the contact name Greg Bensberg, who a quick search reveals is the managing director. The phone number 020 7157 5607 is given with his email greg.bensberg@itv.com.
There is also an email for Sarah Graham, and her Linked In page says she was the assistant to the MD and left in April 2022. I found an advert for a new assistant, but haven't found a name.
Drop Mr Bensberg an email and hopefully it may get passed on to those responsible.
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Sharon Simms: Further to the above, see this from 30 March 2023. Mr Bensberg has stepped down, and his successor is Steve Holebrook:
Steve Holebrook appointed Managing Director of Digital 3&4 | Channel 4
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Sharon Simms: If you or your mother have a Freeview HD TV or box then the HD channels might still be available, including ITV1, Channel 4 and Channel 5. And the TV/boxes are HD then there would seem little point in watching the SD variants. The HD channels are all on one multiplex run by the BBC.
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There are a number of possible causes for said problem, and as such it's not possible to answer it definitively. It requires a methodical and experimental approach. It's quite possible that only once the problem is solved will the cause be known. By which time, of course, it might not matter.
It's not uncommon for a reception issue to affect one or more channels, but not all. It could be a faulty connector, water in the cable running from the aerial, a broken aerial, the aerial having moved and is not facing the right way, or something in the path between the transmitter and receiving aerial. There are other possibilities.
The question then is not what is the cause? but what could the cause be? Being that there are many potential causes, it is probably not possible to take action that would be expected to cure the problem prior to having taken it. One has to be mindful of this. Initiative and some lateral thinking may be invaluable.
That reception was previously good is not evidential fact that the TV is tuned correctly. The self-evident fact is that reception was good previously according to how it was tuned at that time it is not proof positive of tuning being correct.
If the tuning is found to be correct by way of a check, then this is proof-positive that what is on the screen is what is intended to be. If it is not, then the course of action is to correct it.
If the tuning is correct, what might the next course of action be? You might go to your front window and look out. You turn your head a little to the right and you might see a tree in the pavement on the opposite side of the road.
The aerial may be facing the tree which is in the direction of the Mendip transmitter. This tool allows you to put two pins on a map and joins them with a line. With a line drawn from the transmitter to your aerial and satellite image showing, the line might go straight through the canopy of the tree:
Solwise - Surface Elevation Tool | Solwise Ltd
This doesn't mean the reception difficulty is caused by the tree which might exist, but it looks like it might be worth investigating. The hypothesis for the tree being the cause of the difficulty, and only so in the last month or so, is that the tree grows and being summer it has all its leaves.
How might you find out whether it may be the tree affecting reception? I said you need to use initiative. It is currently windy outside, and this may just be very useful here. As the canopy moves, the effect on the signals will move too.
This could be affecting reception on other channels, even where a steady picture is resolved. If there is a tree in line with the aerial, then observing the signal strength screen might be very useful indeed, on all UHF channels, not just C33 (the Sky News one). If the signal strength and/or quality is seen to fluctuate when the wind blows and the branches of the tree move and settles when it is not then that is a very strong pointer to something wind-related and probably the tree, providing there aren't any others.
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tony: Freeview has published here is list of all services on the platform:
Channel listings for Industry Professionals | Freeview
For Rowridge, the multiplexes are:
PSB1 BBC A C24 498MHz
PSB2 D3&4 C27 522MHz
PSB3 BBC B C21+ 474.2MHz
COM4 SDN C25 506MHz
COM5 Arq A C22+ 482.2MHz
COM6 Arq B C28 530MHz
PSB3 and COM5 on C21 and C22 respectively have a positive offset, meaning they are +0.2MHz above the centre of the channel. The receiver may or may not show the ".2", but assume it to mean the same thing.
There is also the local multiplex for Southampton, broadcast on C37 (602MHz) from directional antennas pointing in the direction of Southampton.
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Wednesday 12 July 2023 8:45PM
peter : Perhaps you are thinking of a variable attenuator. An attenuator reduces the level of signal, the opposite of a signal booster (signal amplifier):
Freeview signals: too much of a good thing is bad for you | free and easy